1. Field of the Invention
This invention relates to a CBN grinding wheel containing CBN (Cubic Boron Nitride) grains.
2. Prior Art of the Invention
Vitrified CBN wheels are conventionally used for high efficient grinding of workpieces. Such vitrified CBN wheels have a disadvantage that it gradually becomes difficult to grinding workpieces with a sufficient surface roughness as the cumulative grinding amount by the grinding wheel increases. In a conventional grinding machine, therefore, truing of the grinding wheel is carried out before the surface roughness of workpieces exceeds a predetermined specification limit, so that the initial surface roughness is obtained again.
It is considered that the deterioration of surface roughness is mainly caused by the breakage of the CBN abrasive grains and the drop out of the CBN abrasive grains. To reduce the breakage of the CBN abrasive grains, it is required to use CBN abrasive grains having a high toughness or a low friability. However, when the CBN abrasive grains having a high toughness are used, the drop out of the CBN grains occurs more easily. To reduce the drop out of the CBN abrasive grains, it is also required to increase the amount of the bond to increase the ability of holding the abrasive grains. However, when the amount of the bond is increased, the number of pores in the abrasive layer of the grinding wheel decreases, whereby it becomes difficult to smoothly discharge tips of workpieces from the grinding wheel. This causes deterioration of the form tolerance of workpieces, and surface burn of the workpieces.